The present invention relates to an image display apparatus and a method for operating the same, and a lamp unit for an image display apparatus. In particular, the present invention relates to an image display apparatus, such as a liquid crystal projector, provided with a lamp unit including a high-pressure mercury lamp or a metal halide lamp and a discharge lamp ballast circuit for operating the lamp, and a method for operating the same.
Image display apparatuses such as liquid crystal projector devices are known as means for projecting magnified images of characters, graphics and the like and displaying them. Since such image display apparatuses (or image projection apparatuses) require a predetermined optical output, high-pressure mercury lamps with high brightness are, in general, used widely as light sources. Moreover, as projectors become widespread, there is a growing demand for a brighter and smaller projector.
FIG. 10 schematically shows a cross-sectional structure of a conventional lamp unit 1000 having a high-pressure discharge lamp 101 used for projectors.
The high-pressure discharge lamp 101 shown in FIG. 10 is a high-pressure mercury lamp of alternating current operation type that operates with alternating current. A sealed portion of the lamp 101 is inserted into a neck 1011a of a reflecting mirror 1011, where it is secured with cement and the like. This lamp 101 provided with the reflecting mirror 1011 is housed in a lamp housing 1013, and thus the lamp unit 1000 is constituted.
A pin 311 that serves as a connector is provided in the lamp unit 1000, and the lamp 101 is connected to this pin 311 via cables (leads) 321. FIG. 11A is a perspective view schematically showing the lamp unit 1000, and FIG. 11B is a partially cutaway perspective view schematically showing a projector main body 1100 in which the lamp unit 1000 is to be set.
The lamp unit 1000 can be detached from the projector main body 1100, as shown in FIG. 11B. To achieve such a removable structure, a plug 310 corresponding to the pin 311 provided in the lamp unit 1000 is provided in the main body 1100, and the pin 311 is provided in the lamp unit 1000. The plug 310 and the pin 311 are interchangeable, and the pin can be provided in the main body 1100 and the plug can be provided in the lamp unit 1000.
When the lamp unit 1000 is set in the main body 1100, the pin 311 is coupled to the plug 310. The plug 310 is electrically connected to a ballast circuit (not shown) provided in the main body 1100, and the ballast circuit starts and operates the lamp 101 in the lamp unit 1000. When the lamp unit 1000 is set in the main body 1100, a cooling fan 1104 is situated behind the lamp unit 1000 and a cover 1106 is mounted over the lamp unit 1000. Moreover, an optical system using the lamp 101 as a light source and a system (main system) for controlling the optical system to display images are provided in the main body 1100, and light emitted from the lamp 101 goes through the optical system and a projection lens 1105 to be projected on a screen, where an image is formed.
Next, the circuit structure of a ballast circuit 102 provided in the main body 1100 will be described with reference to FIGS. 12 through 14.
As shown in FIG. 12, the ballast circuit 102 for starting and operating the lamp 101 includes a direct current power 103, a full-bridge inverter circuit 104, which is an inverter circuit, and a start circuit 105. As described above, the ballast circuit 102 is electrically connected to the plug 310 that is provided in the main body 1100 side, and the plug 310 is connected to the full-bridge inverter circuit 104 and the start circuit 105 with high withstand voltage cables 320.
When the lamp unit 1000 is set, the pin 311 is inserted in the plug 310, and the lamp 101 is connected to the pin 311 via the cables 321. The lamp 101 is designed such that the lamp voltage during operation is lower than the maximum output voltage of the direct current power 103. For example, in the case where the maximum output voltage of the direct current power 103 is about 370V, the maximum lamp voltage is about 50V to 250V.
The direct current power 103 is constituted by a step-down chopper circuit that outputs, for example, direct current of a maximum of about 370V in response to an input of direct current of about 370V. The step-down chopper circuit includes a control circuit 115 and a switching element (e.g., transistor, FET, or GTIB) 108. The step-down chopper circuit detects an output voltage with resistors 112 and 113 and an output current with a resister 114, calculates two detection signals with the control circuit 115, and controls on-off of the switching element 108 by an output signal of the control circuit 115 such that the output power of the step-down chopper circuit becomes a predetermined value. Usually, an electrolytic capacitor 111 for smoothing voltage having a relatively large capacitance is connected in parallel to the output terminals of the direct current power 103. In the case where alternating current is input, a rectifying and smoothing circuit for rectifying and smoothing the alternating current input and converting it to direct current is added in a previous stage of the step-down chopper circuit.
The full-bridge inverter circuit 104 is constituted by transistors 117, 118, 119 and 120 and a drive circuit 121, as shown in FIG. 13. In the full-bridge inverter circuit 104, the transistors 117 and 120 and the transistors 118 and 119 are alternately turned on and off by output signals of the drive circuit 121, and thus the output of the step-down chopper circuit is converted to alternating current.
One terminal A of the full-bridge inverter circuit 104 is connected to one terminal TB of a secondary coil (output side coil) constituting the transformer of the start circuit 105 (see FIG. 14) described below, whereas the other terminal B is connected to one end of the lamp via the plug 310 and the pin 311. Moreover, a capacitor 300 is connected in parallel to the both output terminals of the inverter, and this capacitor 300 serves to bypass a high voltage pulse generated in the start circuit 105.
The start circuit 105 is a circuit that generates a high voltage pulse for starting the high-pressure mercury lamp 101. As shown in FIG. 14, the start circuit 105 includes a transformer 208, a resistor 201, a diode 205, a capacitor 206 and a discharge gap 207. Its input terminals are connected to the output terminals of the direct current power 103, and one terminal Tb of the output terminals is connected to the output terminal A of the inverter, and the other terminal Ta is connected to one end of the lamp 101 via the plug 310 and the pin 311, as described above.
The discharge gap 207 has the characteristics that it starts discharge at a voltage that is slightly lower than the output voltage of the direct current power 103 and is higher than the voltage of the lamp in operation (for example, about 350 V), and does not effect discharge (or stops discharge) at a voltage lower than that. Also, the discharge gap 207 has the characteristics that when a pulse voltage of about 350 V (peak value) is applied to a primary coil of the transformer 208, it outputs the high pulse voltage having a peak value of about 10 kV to 15 kV across both the terminals Ta and The of the secondary coil. In such a transformer 208 for generating a high voltage, the primary coil and the secondary coil are wound around cores (e.g., ferrite cores) having a high magnetization capability (not shown).
In addition to this, a timer circuit (not shown) is incorporated in the ballast circuit 102, and the timer circuit has the function of counting the time since the ballast circuit starts operating, and forcefully stopping the operation of the ballast circuit 102 when the lamp 101 fails to operate after a predetermined period (about 3 to 5 seconds). Furthermore, the ballast circuit 102 is also provided with a circuit (not shown) for outputting a signal to indicate the forced stop of the ballast circuit 102 when the lamp 101 did not operate as described above.
In the conventional ballast circuit 102, the direct current power 103, the full-bridge inverter 104, and the start circuit 105 are disposed on the same substrate. The output of this ballast circuit 102 goes through the high withstand voltage cable 320 having a length of about 20 cm to several tens cm and a withstand voltage of about 20 kV, and is supplied to the lamp 101 disposed in the lamp unit 1000 via the plug 310 and the pin 311. The pin 311 is connected to the lamp 101 using a high withstand voltage cable such as the cable 320 as well, and this high withstand voltage cable (321) is a high withstand voltage cable having a length of about 10 cm, which is relatively shorter than the cable 320, and a withstand voltage of about 20 kV.
When the lamp 101 is a discharge lamp of direct current operation type that operates with direct current, the inverter 104 is omitted.
Then, the operation of the ballast circuit 102 will be described.
(1) First, when a signal for starting operation is sent to the direct current power 103 and the full-bridge inverter 104 with a direct current voltage of about 370 V being applied to the direct current power 103, the direct current power (step-down chopper circuit) 103 and the full-bridge inverter 104 start operating.
(2) Then, at the same time, the output voltage (voltage of about 370 V) of the direct current power 103 is input to the start circuit 105.
(3) When the input of the above procedure (2) is performed, the capacitor 206 starts being charged via the resistor 201 and the diode 205.
(4) Then, when the charged voltage of the capacitor 206 reaches a voltage for starting discharge of the discharge gap 207 of about 350 V, the discharge gap 207 discharges, and at that moment, the energy that has been charged in the capacitor is supplied to the primary coil of the transformer 208 at once.
(5) When the energy in the capacitor 206 is discharged, the voltage at the capacitor 206 decreases instantaneously, so that discharge of the discharge gap 207 stops instantaneously.
(6) As a result, a pulse voltage having a peak value of about 370 V is applied to the primary coil of the transformer 208. Thus, a high pulse voltage having a peak value of about 5 kV to 15 kV is output to the secondary coil of the transformer 208, which is, in turn, applied to the lamp 101 via the high withstand voltage cable 320, the plug 310, the pin 311 and the high withstand voltage cable 321.
(7) On the other hand, the capacitor 206 at which the voltage has decreased starts being charged again by the direct current power 103. Therefore, as a result, the above-described operations (3) through (6) are repeated at an interval determined by the time constant of the resistor 201 and the capacitor 206.
(8) When breakdown occurs in the lamp 101 upon application of a pulse voltage and the lamp 101 starts discharge, then a predetermined power is supplied to the lamp 101 through the inverter 104 from the direct current power 103.
(9) This operation is performed by supplying a signal for a voltage that is divided by the resistor 112 and the resistor 113 to detect the lamp voltage and a signal generated by a voltage drop at the resistor 114 for detecting the lamp current to the control circuit 115 of the direct current power 103, processing these signals, and controlling the on-off interval of the switching element 108 such that a power to be supplied to a predetermined lamp becomes a predetermined value.
(10) When the lamp 101 starts operating (breakdown), the operation of the discharge gap 207 stops because the discharge gap 207 is selected such that it operates at a voltage that is slightly lower than the output voltage of the direct current power 103 and is higher than the voltage of the lamp 101 in operation. Therefore, during operation of the lamp, the operation of the start circuit 105 stops.
The ballast circuit 102 operates in this manner. When the lamp fails to operate even after a predetermined time (typically, for 3 seconds to 5 seconds) has passed since the ballast circuit 102 started operating, the ballast circuit forcefully stops its operation, and simultaneously outputs a signal indicating the fact that the lamp does not operate (ballast circuit forced stop). The fact that the lamp fails to operate can be determined easily by the fact that the voltage drop at the resistor 114 that detects the lamp current is less than a predetermined value.
A projector using the above-described conventional ballast circuit 102 and lamp unit 1000 (and lamp 101 housed therein) has the following problems.
First, it is disadvantageous in reducing the size of the projector. Hereinafter, this aspect will be further described.
As projectors become smaller, the size of the ballast circuit 102 is also required to be reduced. However, it is difficult to reduce the size of the transformer (208) in the start circuit 105, so that it is difficult to reduce the size of the entire ballast circuit. For reference purposes, illustrative sizes of the ballast circuit 102 and the start circuit 105 are described as follows. For a class of 100 to 150 W, the size of the ballast circuit 102 is approximately 250 cc, in which the size of the start circuit 105 occupies approximately 25 cc. For a class of 200 W or more, the size of the ballast circuit 102 is approximately 300 cc to 500 cc, in which the size of the start circuit 105 occupies approximately 40 cc. That is to say, about 10% of the space is used only for the first moment (about one second) at which the lamp 101 is lit up.
Since the transformer (208) is a component that basically generates a high voltage, it is impossible to reduce the size of the transformer itself because of the insulation problems. In other words, there is substantially no way other than physically increasing the dimensions to ensure the insulating properties. Therefore, even though the sizes of the other parts can be technically reduced by making them into chips, ICs or modules, the size of the transformer cannot be reduced. Thus, the transformer is an impediment to reduction in size of the ballast circuit 102.
In addition, as seen from FIG. 14, the secondary coil of the transformer 208 is connected in series to the lamp 101. The lamp power of the lamp 101 that is commonly used for the projector is 80 W to 300 W, and in the case where the lamp having the lamp power of 80 W to 300 W is operated, it can be estimated that a current of up to several A (several amperes) flows to the transformer during operation of the lamp. Therefore, it is necessary to use a winding that is thick enough to withstand it for the secondary coil, which makes it further difficult to reduce the size of the transformer 208 (the start circuit 105).
Second, the cost is high and the startability of the lamp is poor.
As shown in FIG. 12, when the start circuit 10S is formed on the ballast circuit substrate, the start circuit 105 may be apart from the lamp 101 by a considerable distance of up to about several tens cm. This is often the case, in particular, in large equipment such as a projection TV. Moreover, even in small projectors, the same problem may arise depending on how the ballast circuit 102 and the lamp 101 are arranged and how wires are provided between the ballast circuit 102 and the lamp 101. Such a problem causes the following disadvantages.
First, it is necessary to use an expensive high withstand voltage cable (cable 320 in FIG. 12) between the start circuit 105 and the lamp 101, and thus the cost is increased.
Next, with respect to the lamp 101, the higher the start voltage is, the higher probability of starting the lamp is. However, the voltage that can be applied to start the lamp is virtually restricted to the withstand voltage of this cable. That is to say, since the maximum withstand voltage of the high withstand voltage cable 320 is about 20 kV to about 30 kV, the voltage that can be applied to start the lamp is virtually restricted to this value. This is a bottleneck in improving the starting characteristics of the lamp.
Furthremore, when this high withstand voltage cable has a length of several tens cm, a start voltage may be attenuated therethrough because the start voltage has a pulse waveform, namely, a waveform rich in high frequency components. In fact, the inventors confirmed by experiment that the attenuation of as much as 1 kV to 2 kV was seen in a certain projector. It seems that this attenuation does not depend on the value of the pulse start voltage that is output from the start circuit 105, but depends on only the type and the length of the cable, and the way of wiring. Therefore, there is no specific means for effective improvement, so that this is a very large disadvantage.
Moreover, as can be guessed from the fact that the voltage is attenuated, the energy of the pulse that has been attenuated results in radiated noise from the cable or voltage leakage to other equipment provided close to the cable, and as a result, causes damage (physically and/or operationally) to the projector main body that is an aggregation of precise electronic equipment and devices. Noise is also generated from the discharge gap in addition to the coils in the start circuit, so that these components also serve as noise sources. The projectors are often used in connection with PCs, and therefore one must be also concerned about damage to the external equipment such as PCs.
Currently, in order to prevent such malfunctions of the projector main body or the external equipment such as PCs, an operation sequence of the projector main body is performed as shown in FIGS. 15A through 15C or FIGS. 15A, 15B and 15D.
The sequence is as follows. As shown in FIGS. 15A through 15D, when a main switch of the projector is turned on (FIG. 15A), first, the start circuit 105 of the ballast circuit 102 starts operating (FIG. 15B), and operation of the other systems in the projector (that is, the main system for projecting images) is stopped while the start circuit 105 is in operation (FIG. 15C), and then, the system is activated after the start circuit 105 stops its operation (FIG. 15C). The fact that the start circuit 105 stops its operation can be determined by detecting the ballast circuit forced stop signal that is to be sent from the ballast circuit 102 being not output.
Alternatively, when the system and the start circuit 105 start operating at the same time, the sequence may be as follows. As shown in FIG. 15D, the operation of the system is forcefully reset and re-activated after the start circuit 105 stops.
Since the operation of the system is delayed from the moment when the main switch is turned on in this manner, consumers often erroneously take this delay for malfunction. Thus, reduction in this system activation time is also required. In particular, for a projector using full digital devices such as DMD, which is especially susceptible to damage such as noise, the start-up time to start the system tends to be set to be delayed. For example, the system starts as long as about 5 seconds after the main switch is turned on. The slow activation of the system is a very large problem. The time of five seconds is a considerably long time from a viewpoint of human psychology, so that some consumers cannot wait for 5 seconds as they erroneously take this slow activation for malfunction, and turn the main switch on again and again. Therefore, this slow activation can be the problem that cannot be ignored, saying that this is only slow activation.
Therefore, with the foregoing in mind, it is a main object of the present invention to provide an image display apparatus whose size is reduced further. It is another object of the present invention to provide an image display apparatus whose activation time can be shortened and a method for operating the same.
An image display apparatus of the present invention includes a lamp unit including a discharge lamp and a reflecting mirror for reflecting light emitted from the discharge lamp; an optical system having the discharge lamp as a light source; and a ballast circuit for starting and operating the discharge lamp. The ballast circuit includes a power circuit portion, an inverter portion, and a start circuit portion, and the start circuit portion of the ballast circuit is electrically connected to the discharge lamp and is separated from the power circuit portion and the inverter portion.
In one preferable embodiment, the power circuit portion and the inverter portion are formed on a same substrate, and the start circuit portion is not disposed on the substrate and is disposed in a position (including a position in the lamp unit) that is closer to the lamp unit than to the substrate.
In one preferable embodiment, the lamp unit includes a lamp housing for housing the discharge lamp and the reflecting mirror. The lamp housing has a shield function. The start circuit portion is provided in the lamp housing having the shield function.
In one preferable embodiment, the lamp unit includes a first connector that is electrically connected to the discharge lamp and is coupled to a second connector electrically connected to at least one of the power circuit portion and the inverter portion. The start circuit portion is provided in the first connector.
It is preferable that a combination of the first connector and the second connector is a combination of an attachment plug and a receptacle.
In one preferable embodiment, the image display apparatus has a structure in which a lamp current supplied from the inverter portion does not flow through a transformer included in the start circuit portion.
In one preferable embodiment, the lamp unit includes the first connector that is electrically connected to the discharge lamp and is coupled to a second connector electrically connected to at least one of the power circuit portion and the inverter portion In addition to the first and the second connectors, the lamp unit includes a third connector that is electrically connected to the start circuit portion. The third connector is coupled to a fourth connector that is electrically connected to a power source.
In one preferable embodiment, the combination of the first connector and the second connector is a combination of an attachment plug and a receptacle. A combination of the third connector and the fourth connector is a combination of an attachment plug and a receptacle.
In one preferable embodiment, the discharge lamp is a high-pressure mercury lamp.
In one preferable embodiment, the image display apparatus includes a digital micromirror device (DMD) in the optical system.
A method for operating an image display apparatus of the present invention is a method for operating an image display apparatus including a lamp unit including a discharge lamp and a reflecting mirror for reflecting light emitted from the discharge lamp; a ballast circuit for starting and operating the discharge lamp; an optical system having the discharge lamp as a light source; and a system for controlling the optical system to display an image. The ballast circuit includes a start circuit portion electrically connected to the discharge lamp. The start circuit portion of the ballast circuit is activated when a power switch included in the image display apparatus is turned on. The system is activated within an operation time during which the start circuit portion is in operation, and a re-activation processing operation is not performed as an activation operation of the system after the operation time is over.
It is preferable that when the power switch is turned on, the start circuit portion of the ballast circuit and the system are activated substantially at the same time, and a time from the turn-on of the power switch to the activation of the system is within about one second.
In one preferable embodiment, the image display apparatus includes a digital micromirror device (DMD) in the optical system.
Another image display apparatus of the present invention includes a lamp unit including a discharge lamp and a reflecting mirror for reflecting light emitted from the discharge lamp; a ballast circuit for starting and operating the discharge lamp; an optical system having the discharge lamp as a light source; and a system for controlling the optical system to display an image. The ballast circuit includes a power circuit portion, an inverter portion, and a start circuit portion. The start circuit portion of the ballast circuit is electrically connected to the discharge lamp and is separated from the power circuit portion and the inverter portion. The start circuit portion of the ballast circuit is activated when a power switch included in the image display apparatus is turned on. The system is activated within an operation time of the start circuit portion, and a re-activation processing operation of the system is not performed as an activation operation of the system after the operation time is over.
A lamp unit of the present invention is a lamp unit used for an image display apparatus including an optical system and a system for controlling the optical system to display an image. The lamp unit includes a discharge lamp; a reflecting mirror for reflecting light emitted from the discharge lamp; and a lamp housing for housing the discharge lamp and the reflecting mirror. A start circuit portion included in a ballast circuit for starting and operating the discharge lamp is separated from a power circuit portion and an inverter portion included in the ballast circuit and is provided in the lamp housing.
In one preferable embodiment, the lamp unit includes a first connector that is electrically connected to the discharge lamp and has a structure that can be coupled to a second connector electrically connected to at least one of the power circuit portion and the inverter portion.
In one preferable embodiment, the start circuit portion outputs a high voltage pulse for starting the discharge lamp to the discharge lamp during operation of the system.
According to the image display apparatus of the present invention, the start circuit portion of the ballast circuit is separated from the power circuit portion and the inverter portion, so that the size of the apparatus can be reduced. When the start circuit portion is disposed in the position that is closer to the lamp unit than to the substrate on which the power circuit portion and the inverter portion are disposed, and in the lamp unit, then the distance between the start circuit and the lamp can be shortened, so that the attenuation of the start voltage can be decreased. As a result, the startability of the lamp can be improved. Moreover, when the start circuit portion is provided in the lamp housing having a shield function, noise from the start circuit portion can be shielded. Therefore, it is possible to activate the system even during operation of the start circuit portion, and consequently it is possible to speed up the activation of the system in the image display apparatus.
When the lamp current does not flow into the transformer included in the start circuit portion, it is possible to use a thin wire for the winding of the transformer, so that the size of the start circuit portion can be further reduced. Moreover, this structure makes it is possible to drive the transformer at high frequency, so that it is preferable in operating a discharge lamp (low start voltage lamp) having a cavity in the sealed portion.
Then, according to the operating method of the image display apparatus of the present invention, the system is activated during the operation time of the start circuit portion and, as the activation operation of the system, the re-activation processing operation is not performed after the above-mentioned operation time is over Thus, the activation time can be reduced. Even if DMD that is susceptible to damage, for example, due to noise, is included in the optical system, the system can be activated substantially upon input of the power switch. Therefore, the present invention provides an advantage especially to an image display apparatus including DMD.